Noninvasive techniques for detection of pathogenic conditions of the human body are an area of growing interest in regards to rapid biosensing and diagnosis of diseases at the point of care (POC). These techniques are preferred for POC diagnosis as handling of traditional samples such as blood requires special skills and exposes the health care worker to possible blood borne pathogens. Ideally, non-invasive methods of diagnostics reduce this risk. To accomplish this, researchers have focused on screening external biological samples (i.e. saliva, urine, hair, sweat, and sputum) for biomarkers that indicate conditions such has diabetes, dehydration, and other diseases. Typical examples of biomarkers are antigens, antibodies, or proteins which require a liquid environment for analysis. As a result, diagnosis of diseases most often requires a liquid biological sample such as those mentioned above. However one class of biomarkers that is known to have associations with certain diseases, and yet has found limited use as a diagnostic tool is volatile organic biomarkers (VOBs). VOBs have been associated with different chronic and infectious diseases including tuberculosis (TB).
As a specific example, conventional methods for tuberculosis (TB) detection are traditionally performed in laboratories or hospitals. For example, the most common method for diagnosis of TB is the acid fast staining of clinical material, which is then followed by a sputum smear microscopy test. However, a disadvantage with the sputum smear test is its poor sensitivity, which is estimated to be at 70%. Additionally, the sensitivity of sputum smear spectroscopy in field settings has been shown to be much lower (e.g. 35%), especially in populations that have high rates of TB and HIV co-infection. Furthermore, drug susceptibility analysis of the mycobacterium cannot be determined from microscopy testing. This assessment is useful in determining the appropriate course of treatment for the patient. For this type of analysis culturing techniques are typically used.
Culturing of mycobacterium from sputum samples is a more sensitive technique. Sputum samples are collected and cultured in either solid media or liquid media looking for the presence of the mycobacterium. Drug resistant strains can be determined using this technique. However this methodology takes time to conduct (3-4 weeks for solid cultures, and 10-14 days for liquid cultures), which makes it difficult to employ in low resource settings that are typically far from testing facilities. Recently, other technologies have been developed including fluorescence microscopy for smear tests (10% more sensitive than light microscopy), LED fluorescent microscopy for inexpensive imaging equipment that can be used in the field without the need for a darkroom, and rapid culturing techniques to reduce incubation time. Despite the improvements that have been made in TB diagnosis, no simple inexpensive POC test is currently available. Accordingly, research continues for a fast, accurate, and inexpensive means for testing for TB.